For you situation, I thought of:
The regexp replies "HOLY CRAP!! ...A TALKING HASH SLICE"
You're setup's not very good though... I have a lot of experience in comedy. Take the scene (a bar) and think of a detail you might find in a bar (a noun or verb). Take whatever it is you thought of (I though of a stool), and think of any aspect/scenario that could possibly relate to it. Take the newly thought of aspect/scenario and combine that with the current scene. If it doesn't sound good, keep doing the same method until you find something that satisfies you. And when you come up with something good, change the setup to fit the punchline better. I came up with:
A man in a bar turns to a gorgeous women and says "hey baby, I got 5 minutes what are you doing?"
The women replies "I'm busying being inconspicuous, but I'm sure if you keep hoping from stool to stool trying to get lucky, you'll find gum under one of them"
in reply to Seeking a good punchline